Other machines for manufacturing objects made of plastic material by means of thermoforming are known. In general, they are machines which have a coil containing a continuous sheet of plastic material, which is pulled in order to make it pass through a heating zone which is determined by suitably arranged heating furnaces; then, under these conditions, the sheet is made to face a performing and molding zone, where it is inserted between preformed components which face respective forming dies for molding. These prior-art machines then operate by cooling, die-forming and subsequent removal and expulsion of each of the thermoformed objects from the die.
These functions, which are known per se, are carried out by the majority of the prior-art machines, of which basically two types can be determined, namely:
a) Those in which, at the same station, where the forming of the object is carried out, the die-forming of the object is also carried out at the same time, in order to then send the object, by means of various mechanisms, to the "stacking" space, called the "stacking station". PA1 b ) Other prior-art machines are those in which the thermoforming is produced in one station and the die-forming is performed in another subsequent station in order to then remove from the mold and stack the objects which are already formed and die-formed at this same station, at another subsequent station or outside of the system.
Although these machines are ever efficient, they are limited in their production capacity. In fact, this limitation lies in the fact that, once the objects are thermoformed, they remain in their dies or molds during the die-forming and cooling stages, with the plastic material machine remaining stopped until the expulsion process ends, immediately after which the molds are newly set up to receive a new section of continuous sheet which is capable of starting a new forming process. As a result, the capacity of the machine is limited by the number of openings per die, presenting disadvantages when the die has more than three thermoforming rows (amounting to the number of openings in a line that the die has for "rows"). This disadvantage lies in obvious imprecisions in accuracy. The extraction of the already thermoformed and die-formed objects presents a high rate of rejection. For this reason, dies with, for example, 48 openings may not be used.
In this case, the machine uses a set of two dies: one die for thermoforming and another die for die-forming; molding is performed in the first station, and die-forming is performed in the second station. The advantage in this case is that dies with three or more rows can be used. It so happens that the molded objects, still without die-forming, leave the molding die to enter the die-forming die, and imprecisions in the die-formed edges of the objects are produced there, which lead to rejection.
In addition to that mentioned above, the disadvantage which is prominent in both cases is the limitation of production which causes delay times in the machines in each of the "stations" stages of the process. In fact, the stations consist of 1) the time for feeding the continuous sheet until it is arranged in the thermoforming and molding sector; 2) the preforming time; 3) the thermoforming time; 4) the delay time during the process for cooling the molded objects; 5) the time which passes for the die-forming; 6) the time which passes for the expulsion of the pieces and their stacking. Once all of these stages have elapsed, the machine is then again able to start a new cycle.